Prosthetic foot with tunable performance

ABSTRACT

A prosthetic foot ( 70 ) incorporates a foot keel ( 71 ) and a calf shank ( 72 ) connected to the foot keel to form an ankle joint area of the prosthetic foot. The foot keel has forefoot and hindfoot portions and an upwardly arched midfoot portion extending between the forefoot and midfoot portions. The calf shank includes a downward convexly curved lower end which is secured to the foot keel by way of a coupling element ( 73 ). The lower end of the calf shank extends upwardly, and initially anteriorly therefrom into a reversely curved portion ( 75 ) of the calf shank leading to an upstanding upper end thereof.

RELATED APPLICATIONS

This application is a U.S. national stage application filed under 35U.S.C. §371 of international application PCT/US02/09571 and acontinuation in part of U.S. application Ser. No. 09/820,895, filed Mar.30, 2001, now U.S. Pat. No. 6,562,075 issued May 13, 2003, the priorityof which is claimed.

TECHNICAL FIELD

The present invention relates to a high performance prosthetic footproviding improved dynamic response capabilities as these capabilitiesrelate to applied force mechanics.

BACKGROUND ART

A jointless artificial foot for a leg prosthesis is disclosed by Martinet al. in U.S. Pat. No. 5,897,594. Unlike earlier solutions wherein theartificial foot has a rigid construction provided with a joint in orderto imitate the function of the ankle, the jointless artificial foot ofMartin et al. employs a resilient foot insert which is arranged inside afoot molding. The insert is of approximately C-shaped design inlongitudinal section, with the opening to the rear, and takes up theprosthesis load with its upper C-limb and via its lower C-limb transmitsthat load to a leaf spring connected thereto. The leaf spring as seenfrom the underside is of convex design and extends approximatelyparallel to the sole region, forward beyond the foot insert into thefoot-tip region. The Martin et al. invention is based on the object ofimproving the jointless artificial foot with regard to damping theimpact of the heel, the elasticity, the heel-to-toe walking and thelateral stability, in order thus to permit the wearer to walk in anatural manner, the intention being to allow the wearer both to walknormally and also to carry out physical exercise and to play sports.However, the dynamic response characteristics of this known artificialfoot are limited. There is a need for a higher performance prostheticfoot having improved applied mechanics design features which can improveamputee athletic performances involving activities such as running,jumping, sprinting, starting, stopping and cutting, for example.

Other prosthetic feet have been proposed by Van L. Phillips whichallegedly provide an amputee with an agility and mobility to engage in awide variety of activities which were precluded in the past because ofthe structural limitations and corresponding performances of prior artprostheses. Running, jumping and other activities are allegedlysustained by these known feet which, reportedly, may be utilized in thesame manner as the normal foot of the wearer. See U.S. Pat. Nos.6,071,313; 5,993,488; 5,899,944; 5,800,569; 5,800,568; 5,728,177;5,728,176; 5,824,112; 5,593,457 5,514,185; 5,181,932; and 4,822,363, forexample.

DISCLOSURE OF INVENTION

In order to allow the amputee athlete to attain a higher level ofperformance, there is a need for a high performance prosthetic foothaving improved applied mechanics, which foot can out perform the humanfoot and also out perform the prior art prosthetic feet. It is ofinterest to the amputee athlete to have a high performance prostheticfoot having improved applied mechanics, high low dynamic response, andalignment adjustability that can be fine tuned to improve the horizontaland vertical components of activities which can be task specific innature.

The prosthetic foot of the present invention addresses these needs.According to an example embodiment disclosed herein, the prosthetic footof the invention comprises a longitudinally extending foot keel having aforefoot portion at one end, a hindfoot portion at an opposite end and arelatively long midfoot portion extending between and upwardly archedfrom the forefoot and hindfoot portions. A calf shank including adownward convexly curved lower end is also provided. An adjustablefastening arrangement attaches the curved lower end of the calf shank tothe upwardly arched midfoot portion of the foot keel to form an anklejoint area of the prosthetic foot.

The adjustable fastening arrangement permits adjustment of the alignmentof the calf shank and the foot keel with respect to one another in thelongitudinal direction of the foot keel for tuning the performance ofthe prosthetic foot. By adjusting the alignment of the opposed upwardlyarched midfoot portion of the foot keel and the downward convexly curvedlower end of the calf shank with respect to one another in thelongitudinal direction of the foot keel, the dynamic responsecharacteristics and motion outcomes of the foot are changed to be taskspecific in relation to the needed/desired horizontal and verticallinear velocities. A multi-use prosthetic foot is disclosed having highand low dynamic response capabilities, as well as biplanar motioncharacteristics, which improve the functional outcomes of amputeesparticipating in sporting and/or recreational activities. A prostheticfoot especially for sprinting is also disclosed.

The calf shank can have its lower end downward, convexly curved andextending upwardly, and initially anteriorly into a reversely curvedportion of the calf shank leading to an upstanding upper end thereof.With this construction, a cosmetic covering in the shape of a human footand lower leg easily located over the foot keel and at least the lowerend of the calf shank with the calf shank rising upwardly from the footkeel within the lower leg covering. A plurality of longitudinallyextending grooves and fins formed on the posteriorly facing surface ofthe reversely curved portion facilitate resilient compression of thecalf shank while resisting expansion thereof in response to forces onthe calf shank during use of the prosthetic foot.

These and other objects, features and advantages of the presentinvention become more apparent from a consideration of the followingdetailed description of disclosed example embodiments of the inventionand the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration representing the two adjacent radiiof curvatures R₁ and R₂, one against the other, of a foot keel and calfshank of a prosthetic foot of the invention which creates a dynamicresponse capability and motion outcome of the foot in gait in thedirection of arrow B which is perpendicular to the tangential line Aconnecting the two radii.

FIG. 2 is a view similar to FIG. 1 but showing the alignment of the tworadii having been changed in the prosthetic foot according to theinvention to increase the horizontal component and decrease the verticalcomponent of the dynamic response capability and motion outcome of thefoot in gait so that arrow B₁, perpendicular to tangential line A₁, ismore horizontally directed than is the case depicted in FIG. 1.

FIG. 3 is a side view of a prosthetic foot according to an exampleembodiment of the invention with pylon adapter and pylon connectedthereto for securing the foot to the lower leg of an amputee.

FIG. 4 is a front view of the prosthetic foot with pylon adapter andpylon of FIG. 3.

FIG. 5 is a top view of the embodiment of FIGS. 3 and 4.

FIG. 6 is a side view of another foot keel of the invention, especiallyfor sprinting, which may be used in the prosthetic foot of theinvention.

FIG. 7 is a top view of the foot keel of FIG. 6.

FIG. 8 is a bottom view of the foot keel in the prosthetic foot in FIG.3 which. provides high low dynamic response characteristics as well asbiplanar motion capabilities.

FIG. 9 is a side view of an additional foot keel of the invention forthe prosthetic foot particularly useful for sprinting by an amputee thathas had a Symes amputation of the foot.

FIG. 10 is a top view of the foot keel of FIG. 9.

FIG. 11 is a further variation of foot keel for the prosthetic foot ofthe invention for a Symes amputee, the foot keel providing theprosthetic foot with high low dynamic response characteristics as wellas biplanar motion capabilities.

FIG. 12 is a top view of the foot keel of FIG. 11.

FIG. 13 is a side view of a foot keel of the invention wherein thethickness of the keel tapers, e.g., is progressively reduced, from themidfoot portion to the hindfoot portion of the keel.

FIG. 14 is a side view of another form of the foot keel wherein thethickness tapers from the midfoot toward both the forefoot and hindfootof the keel.

FIG. 15 is a side view from slightly above and to the front of aparabola shaped calf shank of the prosthetic foot of the invention, thethickness of the calf shank tapering toward its upper end.

FIG. 16 is a side view like FIG. 15 but showing another calf shanktapered from the middle towards both its upper and lower ends.

FIG. 17 is a side view of a C-shaped calf shank for the prosthetic foot,the calf shank thickness tapering from the middle towards both its upperand lower ends.

FIG. 18, is a side view of another example of a C-shaped calf shank forthe prosthetic foot, the thickness of the calf shank being progressivelyreduced from its midportion to its upper end.

FIG. 19 is a side view of an S-shaped calf shank for the prostheticfoot, both ends being progressively reduced in thickness from the middlethereof.

FIG. 20 is a further example of an S-shaped calf shank which is taperedin thickness only at its upper end.

FIG. 21 is a side view of a J-shaped calf shank, tapered at each end,for the prosthetic foot of the invention.

FIG. 22 is a view like FIG. 21 but showing a J-shaped calf shank whichis progressively reduced in thickness towards only its upper end.

FIG. 23 is a side view, from slightly above, of an aluminum or plasticcoupling element used in the adjustable fastening arrangement of theinvention for attaching the calf shank to the foot keel as shown in FIG.3.

FIG. 24 is a view from the side and slightly to the front of a pylonadapter used on the prosthetic foot of FIGS. 3–5 for connecting the footto a pylon to be attached to an amputee's leg.

FIG. 25 is a side view of another prosthetic foot of the inventionsimilar to that in FIG. 3, but showing use of a coupling element withtwo releasable fasteners spaced longitudinally connecting the element tothe calf shank and foot keel, respectively.

FIG. 26 is an enlarged side view of the coupling element in FIG. 25.

FIG. 27 is an enlarged side view of the calf shank of the prostheticfoot of FIG. 25.

FIG. 28 is a side view of another calf shank of the prosthetic foot ofthe invention, having a reversely curved portion above the generallyparabola shaped lower end.

FIG. 29 is a left side view of the calf shank of FIG. 28.

FIG. 30 is a right side view of the calf shank of FIG. 28 showing aplurality of S-shaped grooves and fins extending longitudinally on theposteriorly facing, reversely curved portion of the calf shank.

FIG. 31 is a sectional view of the calf shank of FIGS. 28–30 taken alongthe line 31—31 in FIG. 28.

FIG. 32 is a. side view of another embodiment of the prosthetic foot ofthe invention wherein the calf shank of FIGS. 28–31 is utilized within acosmetic covering of the foot.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to the drawings, a prosthetic foot 1 in the exampleembodiment of FIGS. 3–5 is seen to comprise a longitudinally extendingfoot keel 2 having a forefoot portion 3 at one end, a hindfoot portion 4at an opposite end and a relatively long midfoot portion 5 extendingbetween and upwardly arched from the forefoot and hindfoot portions. Themidfoot portion 5 is upward convexly curved over its entire longitudinalextent between the forefoot and hindfoot portions in the exampleembodiment.

An upstanding calf shank 6 of the foot 1 is attached at a portion of adownward convexly curved lower end 7 thereof to a proximate, posteriorsurface of the keel midfoot portion 5 by way of a releasable fastener 8and coupling element 11. The fastener 8 is a single bolt with nut andwashers in the example embodiment, but could be a releasable clamp orother fastener for securely positioning and retaining the calf shank onthe foot keel when the fastener is tightened.

A longitudinally extending opening 9 is formed in a proximate, posteriorsurface of the keel midfoot portion 5, see FIG. 8. A longitudinallyextending opening 10 is also formed in the curved lower end 7 of thecalf shank 6 like that shown in FIG. 15, for example. The releasablefastener 8 extends through the openings 9 and 10 to permit adjusting thealignment of the calf shank and the foot keel with respect to oneanother in the longitudinal direction, A—A in FIG. 5, when the fastener8 is loosened or released for tuning the performance of the prostheticfoot to be task specific. Thus, the fastener 8, coupling element 11 andlongitudinally extending openings 9 and 10 constitute an adjustablefastening arrangement for attaching the calf shank to the foot keel toform an ankle joint area of the prosthetic foot.

The effect of adjusting the alignment of the calf shank 6 and foot keel2 are seen from a consideration of FIGS. 1 and 2, wherein the two radiiR₁ and R₂, one next to another, represent the adjacent, facing, domed orconvexly curved surfaces of the foot keel midportion 5 and the calfshank 6. When two such radii are considered one next to another, motioncapability exists perpendicular to a tangential line, A in FIG. 1, A₁ inFIG. 2, drawn between the two radii. The interrelationship between thesetwo radii determines a direction of motion outcomes. As a consequence,dynamic response force application of the foot 1 is dependent on thisrelationship. The larger the radius of a concavity, the more dynamicresponse capability. However, the tighter a radius, the quicker itresponds.

The alignment capability of the calf shank and foot keel in theprosthetic foot of the invention allows the radii to be shifted so thathorizontal or vertical linear velocities with the foot in athleticactivities are affected. For example, to improve the horizontal linearvelocity capability of the prosthetic foot 1, an alignment change can bemade to affect the relationship of the calf shank's radius and the footkeel radius. That is, to improve the horizontal linear velocitycharacteristic, the bottom radius R₂, of the foot keel, is made moredistal than its start position, FIG. 2 as compared with FIG. 1. Thischanges the dynamic response characteristics and motion outcomes of thefoot 1 to be more horizontally directed and as a result greaterhorizontal linear velocity can be achieved with the same applied forces.

The amputee can, through practice, find a setting for each activity thatmeets his/her needs as these needs relate to horizontal and verticallinear velocities. A jumper and a basketball player, for example, needmore vertical lift than a sprint runner. The coupling element 11 is aplastic or metal alloy, such as aluminum, alignment coupling (see FIGS.3, 4 and 23) sandwiched between the attached foot keel 2 and calf shank6. The releasable fastener 8 extends through a hole 12 in the couplingelement. The coupling element extends along the attached portion of thecalf shank and the proximate, posterior surface of the keel midfootportion 5.

The curved lower end 7 of the calf shank 6 is in the shape of a parabolawith the smallest radius of curvature of the parabola located at thelower end and extending upwardly, and initially anteriorly in theparabola shape. A posteriorly facing concavity is formed by thecurvature of the calf shank as depicted in FIG. 3. The parabola shape isadvantageous in that it has increased dynamic response characteristicsin creating both improved horizontal linear velocity associated with therelatively larger radii proximal terminal end thereof, while having asmaller radius of curvature at its lower end for quicker responsecharacteristics. The larger radii of curvature at the upper end of theparabola shape enable the tangential line A, explained with reference toFIGS. 1 and 2, to remain more vertically oriented with changes inalignment, which creates improved horizontal linear velocity.

A pylon adapter 13 is connected to the upper end of the calf shank 6 byfasteners 14. The adapter 13 in turn is secured to the lower end ofpylon 15 by fasteners 16. Pylon 15 is secured to the lower limb of theamputee by a supporting structure (not shown) attached to the leg stump.

The forefoot, midfoot and hindfoot portions of the foot keel 2 areformed of a single piece of resilient material in the exampleembodiment. For example, a solid piece of material, plastic in nature,having shape-retaining characteristics when deflected by the groundreaction forces can be employed. In particular, a high strengthgraphite, laminated with epoxy thermosetting resins, or extruded plasticutilized under the tradename of Delran, or degassed polyurethanecopolymers, may be used to form the foot keel and also the calf shank.The functional qualities associated with these materials afford highstrength with low weight and minimal creep. The thermosetting epoxyresins are laminated under vacuum utilizing prosthetic industrystandards. The polyurethane copolymers can be poured into negative moldsand the extruded plastic can be machined. Each material of use has itsadvantages and disadvantages.

The resilient material's physical properties as they relate tostiffness, flexibility and strength are all determined by the thicknessof the material. A thinner material will deflect easier than a thickermaterial of the same density. The material utilized, as well as thephysical properties, are associated with the stiffness to flexibilitycharacteristics in the prosthetic keel and calf shank. The thickness ofthe keel and calf shank are uniform or symmetrical in the exampleembodiment of FIGS. 3–5, but the thickness along the length of thesecomponents can be varied as discussed below, such as by making thehindfoot and forefoot areas thinner and more responsive to deflection inthe midfoot region.

To aid in providing the prosthetic foot 1 with a high low dynamicresponse capability, the midfoot portion 5 is formed by a longitudinalarch such that the medial aspect of the longitudinal arch has arelatively higher dynamic response capability than the lateral aspect ofthe longitudinal arch. For this purpose, in the example embodiment, themedial aspect of the longitudinal arch concavity is larger in radiusthan the lateral aspect thereof. The posterior end 17 of the hindfootportion 4 is shaped in an upwardly curved arch that reacts to groundreaction forces during heel strike by compressing for shock absorption.The heel formed by the hindfoot portion 4 is formed with a posteriorlateral corner 18 which is more posterior and lateral than the medialcorner 19 to encourage hindfoot eversion during initial contact phase ofgait. The anterior end 20 of the forefoot portion 3 is shaped in anupwardly curved arch to simulate the human toes being dorsiflexed in theheel rise toe off position of the late stance phase of gait. Rubber orfoam pads 53 and 54 are provided on the lower forefoot and hindfoot ascushions.

Improved biplanar motion capability of the prosthetic foot is created bymedial and lateral expansion joint holes 21 and 22 extending through theforefoot portion 3 between dorsal and plantar surfaces thereof.Expansion joints 23 and 24 extend forward from respect ones of the holesto the anterior edge of the forefoot portion to form medial, middle andlateral expansion struts 25–27 which create improved biplanar motioncapability of the forefoot portion of the foot keel. The expansion jointholes 21 and 22 are located along a line, B—B in FIG. 5, in thetransverse plane which extends at an angle a of 350 to the longitudinalaxis A—A of the foot keel with the medial expansion joint hole 21 moreanterior than the lateral expansion joint hole 22. The expansion jointholes 21 and 22 as projected on a sagittal plane are inclined at anangle of 450 to the transverse plane with the dorsal aspect of the holesbeing more anterior than the plantar aspect. With this arrangement, thedistance from the releasable fastener 8 to the lateral expansion jointhole 22 is shorter than the distance from the releasable fastener to themedial expansion joint hole 21 such that the lateral portion of theprosthetic foot 1 has a shorter toe lever than the medial for enablingmidfoot high and low dynamic response.

The anterior of the hindfoot portion 4 of the foot keel 2 furtherincludes an expansion joint hole 28 extending through the hindfootportion 4 between dorsal and plantar surfaces thereof. An expansionjoint 29 extends posteriorly from the hole 28 to the posterior edge ofthe hindfoot portion to form expansion struts 30 and 31. These createimproved biplanar motion capability of the hindfoot portion of the foot.

A dorsal aspect of the midfoot portion 5 and the forefoot portion 3 ofthe foot keel 2 form the upwardly facing concavity, 32 in FIG. 3, sothat it mimics in function the fifth ray axis of motion of a human foot.That is, the concavity 32 has a longitudinal axis C—C which is orientedat an angle 13 of 15° to 35° to the longitudinal axis A—A of the footkeel with the medial being more anterior than the lateral to encouragefifth ray motion in gait as in the oblique low gear axis of rotation ofthe second to fifth metatarsals in the human foot.

The importance of biplanar motion capability can be appreciated when anamputee walks on uneven terrain or when the athlete cuts medially orlaterally on the foot. The direction of the ground force vector changesfrom being sagittally oriented to having a frontal plane component. Theground will push medially in opposite direction to the foot pushinglaterally. As a consequence to this, the calf shank leans medially andweight is applied to the medial structure of the foot keel. In responseto these pressures, the medial expansion joint struts 25 and 31 of thefoot keel 2 dorsiflex (deflect upward) and invert, and the lateralexpansion joint struts 27 and 30 plantar flex (deflect downwards) andinvert. This motion tries to put the plantar surface of the foot flat onthe ground (plantar grade).

Another foot keel 33 of the invention, especially for sprinting, may beused in the prosthetic foot of the invention, see FIGS. 6 and 7. Thebody's center of gravity in a sprint becomes exclusively sagittal planeoriented. The prosthetic foot does not need to have a low dynamicresponse characteristic. As a consequence, the 15° to 35° externalrotation orientation of the longitudinal axis of the forefoot, midfootconcavity as in foot keel 2 is not needed. Rather, the concavity'slongitudinal axis D—D orientation should become parallel to the frontalplane as depicted .in FIGS. 6 and 7. This makes the sprint foot respondin a sagittal direction only. Further, the orientation of the expansionjoint holes 34 and 35 in the forefoot and midfoot portions, along lineE—E, is parallel to the frontal plane, i.e., the lateral hole 35 ismoved anteriorly and in line with the medial hole 34 and parallel to thefrontal plane. The anterior terminal end 36 of the foot keel 33 is alsomade parallel to the frontal plane. The posterior terminal heel area 37of the foot keel is also parallel to the frontal plane. Thesemodifications effect in a negative way the multi-use capabilities of theprosthetic foot. However, its performance characteristics become taskspecific. Another variation in the sprint foot keel 33 is in the toe,ray region of the forefoot portion of the foot where 15° of dorsiflexionin the foot keel 2 are increased to 25–40° of dorsiflexion in foot keel33.

FIGS. 9 and 10 show an additional foot keel 38 of the invention for theprosthetic foot particularly useful for sprinting by an amputee that hashad a Symes amputation of the foot. For this purpose, the midfootportion of the foot keel 38 includes a posterior, upwardly facingconcavity 39 in which the curved lower end of the calf shank is attachedto the foot keel by way of the releasable fastener. This foot keel canbe utilized by all lower extremity amputees. The foot keel 38accommodates the longer residual limb associated with the Symes levelamputee. Its performance characteristics are distinctively quicker indynamic response capabilities. Its use is not specific to this level ofamputation. It can be utilized on all transtibial and transfemoralamputations. The foot keel 40 in the example embodiment of FIGS. 11 and12 also has a concavity 41 for a Symes amputee, the foot keel providingthe prosthetic foot with high low dynamic response characteristic aswell as biplanar motion capabilities like those of the exampleembodiment in FIGS. 3–5 and 8.

The functional characteristics of the several foot keels for theprosthetic foot 1 are associated with the shape and design features asthey relate to concavities, convexities, radii size, expansion,compression, and material physical properties—all of these propertiesrelating, to reacting to, ground forces in walking, running and jumpingactivities.

The foot keel 42 in FIG. 13 is like that in the example embodiment ofFIGS. 3–5 and 8, except that the thickness of the foot keel is taperedfrom the midfoot portion to the posterior of the hindfoot. The foot keel43 in FIG. 14 has its thickness progressively reduced or tapered at bothits anterior and posterior ends. Similar variations in thickness areshown in the calf shank 44 of FIG. 14 and the calf shank 45 of FIG. 16which may be used in the prosthetic foot 1. Each design of the foot keeland calf shank create different functional outcomes, as these functionoutcomes relate to the horizontal and vertical linear velocities whichare specific to improving performance in varied athletic related tasks.The capability of multiple calf shank configurations and adjustments insettings between the foot keel and the calf shank create a prostheticfoot calf shank relationship that allows the amputee and/or theprosthetist the ability to tune the prosthetic foot for maximumperformance in a selected one of a wide variety of sport andrecreational activities.

Other calf shanks for the prosthetic foot 1 are illustrated in FIGS.17–22 and include C-shaped calf shanks 46 and 47, S-shaped calf shanks48 and 49 and J-shaped calf shanks 50 and 51. The upper end of the calfshank could also have a straight vertical end with a pyramid attachmentplate attached to this proximal terminal end. A male pyramid could bebolted to and through this vertical end of the calf shank. Plastic oraluminum fillers to accept the proximal male pyramid and the distal footkeel could also be provided in the elongated openings at the proximaland distal ends of the calf shank. The prosthetic foot of the inventionis a modular system preferably constructed with standardized units ordimensions for flexibility and variety in use.

All track related running activities take place in a counter-clockwisedirection. Another, optional feature of the invention takes into accountthe forces acting on the foot advanced along such a curved path.Centripetal acceleration acts toward the center of rotation where anobject moves along a curved path. Newton's third law is applied forenergy action. There is an equal and opposite reaction. Thus, for every“center seeking” force, there is a “center fleeing” force. Thecentripetal force acts toward the center of rotation and the centrifugalforce, the reaction force, acts away from the center of rotation. If anathlete is running around the curve on the track, the centripetal forcepulls the runner toward the center of the curve while the centrifugalforce pulls away from the center of the curve. To counteract thecentrifugal force which tries to lean the runner outward, the runnerleans inward. If the direction of rotation of the runner on the track isalways counter-clockwise, then the left side is the inside of the track.As. a consequence, according to a feature of the present invention, theleft side of the right and left prosthetic foot calf shanks can be madethinner than the right side and the amputee runner's curve performancecould be improved.

The foot keels 2, 33, 38, 42 and 43 in the several embodiments, are each29 cm long with the proportions of the shoe 1 shown to scale in FIGS. 3,4 and 5, and in the several views of the different calf shanks and footkeels. However, as will be readily understood by the skilled artisan,the specific dimensions of the prosthetic foot can be varied dependingon the size, weight and other characteristics of the amputee beingfitted with the foot.

The operation of the prosthetic foot 1 in walking and running stancephase gait cycles will now be considered. Newton's three laws of motion,that relate to law of inertia, acceleration and action-reaction, are thebasis for movement kinematics in the foot 2. From Newton's third law,the law of action-reaction, it is known that the ground pushes on thefoot in a direction equal and opposite to the direction the foot pusheson the ground. These are known as ground reaction forces. Manyscientific studies have been done on human gait, running and jumpingactivities. Force plate studies show us that Newton's third law occursin gait. From these studies, we know the direction the ground pushes onthe foot.

The stance phase of walking/running activities can be further brokendown into deceleration and acceleration phases. When the prosthetic foottouches the ground, the foot pushes anteriorly on the ground and theground pushes back in an equal and opposite direction—that is to say theground pushes posteriorly on the prosthetic foot. This force makes theprosthetic foot move. The stance phase analysis of walking and runningactivities begins with the contact point being the posterior lateralcorner 18, FIGS. 3 and 18, which is offset more posteriorly andlaterally than the medial side of the foot. This offset at initialcontact causes the foot to evert and the calf shank to plantar flex. Thecalf shank always seeks a position that transfers the body weightthrough its shank, e.g., it tends to have its long vertical member in aposition to oppose the ground forces. This is why it movesposteriorly—plantar flexes to oppose the ground reaction force which ispushing posteriorly on the foot. The ground forces cause the calf shankto compress with the proximal end moving posteriorly. The calf shanklower tight radius compresses simulating human ankle joint plantarflexion and the forefoot is lowered by compression to the ground. At thesame time, the posterior aspect of the top of the foot keel 2 compressesupward through compression. Both of these compressive forces act asshock absorbers. This shock absorption is further enhanced by the offsetposterior lateral heel 18 which causes the foot to evert, which alsoacts as a shock absorber, once the calf shank has stopped moving intoplantar flexion and with the ground pushing posteriorly on the foot.

The compressed members of the foot keel and calf shank then start tounload—that is they seek their original shape and the stored energy isreleased—which causes the calf shank proximal end to move anteriorly inan accelerated manner. As the calf shank approaches its verticalstarting position, the ground forces change from pushing posteriorly topushing vertically upward against the foot. Since the prosthetic foothas posterior and anterior plantar surface weight bearing areas andthese areas are connected by a non-weight bearing long arch shapedmidportion, the vertically directed forces from the prosthesis cause thelong arch shaped midportion to load by expansion. The posterior andanterior weight—bearing surfaces diverge. These vertically directedforces are being stored in the long arch midportion of the foot—as theground forces move from being vertical in nature to anteriorly directed.The calf shank expands—simulating ankle dorsiflexion. This causes theprosthetic foot to pivot off of the anterior plantar weight-bearingsurface. The hindfoot long arch changes from being compressed to beingexpanded. This releases the stored vertical compressed force energy intoimproved expansion capabilities.

The long arch of the foot keel and the calf shank resist expansion oftheir respective structures. As a consequence, the calf shank anteriorprogression is arrested and the foot starts to pivot off the anteriorplantar surface weight—bearing area. The expansion of the midfootportion of the foot keel has as high and low response capability in thecase of the foot keels in the example embodiments of FIGS. 3–5 and 8,FIGS. 11 and 12, FIG. 13 and FIG. 14. Since the midfoot forefoottransitional area of these foot keels is deviated 25° to 35° externallyfrom the long axis of the foot, the medial long arch is longer than thelateral long arch. This is important because in the normal foot, duringacceleration or deceleration, the medial aspect of the foot is used.

The prosthetic foot longer medial arch has greater dynamic responsecharacteristic than the lateral. The lateral shorter toe lever isutilized when walking or running at slower speeds. The body's center ofgravity moves through space in a sinusoidal curve. It moves medial,lateral, proximal and distal. When walking or running at slower speeds,the body's center of gravity moves more medial and lateral than whenwalking or running fast. In addition, momentum or inertia is less andthe ability to overcome a higher dynamic response capability is less.The prosthetic foot of the invention is adapted to accommodate theseprinciples in applied mechanics.

As the ground forces push anteriorly on the prosthetic foot which ispushing posteriorly on the ground, as the heel begins to rise theanterior portion of the long arch of the midfoot portion is contoured toapply these posteriorly directed forces perpendicular to its plantarsurface. This is the most effective and efficient way to apply theseforces. The same can be said about the posterior hindfoot portion of theprosthetic foot. It is also shaped so that the posteriorly directedground forces at initial contact are opposed with the foot keel'splantar surface being perpendicular to their applied force direction.

In the later stages of heel rise, toe off walking and runningactivities, the ray region of the forefoot portion is dorsiflexed15°–35°. This upwardly extending arc allows the anteriorly directedground forces to compress this region of the foot. This compression isless resisted than expansion and a smooth transition occurs to the swingphase of gait and running with the prosthetic foot. In later stages ofstance phase of gait, the expanded calf shank and the expanded midfootlong arch release their stored energy adding to the propulsion of theamputee's body's center of gravity.

The posterior aspect of the hindfoot and the forefoot region of the footkeel incorporate expansion joint holes and expansion joint struts inseveral of the embodiments as noted previously. The orientation of theexpansion joint holes act as a mitered hinge and biplanar motioncapabilities are improved for improving the total contactcharacteristics of the plantar surface of the foot when walking onuneven terrain.

The Symes foot keels in FIGS. 9–12 are distinctively different indynamic response capabilities—as these capabilities are associated withwalking, running and jumping activities. These foot keels differ in fourdistinct features. These include the presence of a concavity in theproximate, posterior of the midfoot portion for accommodating the Symesdistal residual limb shape better than a flat surface. The alignmentconcavity requires that the corresponding anterior and posterior radiiof the arched foot keel midportion be more aggressive and smaller insize. As a consequence, all of the midfoot long arch radii and thehindfoot radii are tighter and smaller. This significantly affects thedynamic response characteristics. The smaller radii create lesspotential for a dynamic response. However, the prosthetic foot respondsquicker to all of the aforementioned walking, running and jumping groundforces. The result is a quicker foot with less dynamic response.

Improved task specific athletic performance can be achieved withalignment changes using the prosthetic foot of the invention, as thesealignment changes affect the vertical and horizontal components of eachtask. The human foot is a multi-functional unit—it walks, runs andjumps. The human tibia fibula calf shank structure on the other hand isnot a multi-functional unit. It is a simple lever which applies itsforces in walking, running and jumping activities parallel to its longproximal—distal orientation. It is a non-compressible structure and ithas no potential to store energy. On the other hand, the prosthetic footof the invention has dynamic response capabilities, as these dynamicresponse capabilities are associated with the horizontal and verticallinear velocity components of athletic walking, running and jumpingactivities and out-performing the human tibia and fibula. As aconsequence, the possibility exists to improve amputee athleticperformance. For this purpose, according to the present invention, thefastener 8 is loosened and the alignment of the calf shank and the footkeel with respect to one another is adjusted in the longitudinaldirection of the foot keel. Such a change is shown in connection withFIGS. 1 and 2. The calf shank is then secured to the foot keel in theadjusted position with the fastener 8. During this adjustment, the boltof the fastener 8 slides relative to one or both of the opposed,relatively longer, longitudinally extending openings 9 and 10 in thefoot keel and calf shank, respectively.

An alignment change that improves the performance characteristic of arunner who makes initial contact with the ground with the foot flat asin sprinting, for example, is one wherein the foot keel is slid anteriorrelative to the calf shank and the foot plantar flexed on the calfshank. This new relationship improves the horizontal component ofrunning. That is, with the calf shank plantar flexed to the foot, andthe foot making contact with the ground in a foot flat position asopposed to initially heel contact, the ground immediately pushesposteriorly on the foot that is pushing anteriorly on the ground. Thiscauses the calf shank to move rapidly forward (by expanding) anddownwardly. Dynamic response forces are created by expansion whichresists the calf shank's direction of initial movement. As aconsequence, the foot pivots over the metatarsal plantar surfaceweight—bearing area. This causes the midfoot region of the keel toexpand which is resisted more than compression. The net effect of thecalf shank expansion and the midfoot expansion is that further anteriorprogression of the calf shank is resisted which allows the kneeextenders and hip extenders in the user's body to move the body's centerof gravity forward and proximal in a more efficient manner (i.e.,improved horizontal velocity). In this case, more forward than up thanin the case of a heel toe runner whose calf shank's forward progressionis less resisted by the calf shank starting more dorsiflexed (vertical)than a foot flat runner.

To analyze the sprint foot in function, an. alignment change of the calfshank and foot keel is made. Advantage is taken of the foot keel havingall of its concavities with their longitudinal axis orientation parallelto the frontal plane. The calf shank is plantar flexed and slidposterior on the foot keel. This lowers the distal circles even furtherthan on the flat foot runner with the multi-use foot keel like that inFIGS. 3–5 and 8, for example. As a consequence, there is even greaterhorizontal motion potential and the dynamic response is directed intothis improved horizontal capability.

The sprinters have increased range of motion, forces and momentum(inertia)—momentum being a prime mover. Since their stance phasedeceleration phase is shorter than their acceleration phase, increasedhorizontal linear velocities are achieved. This means that at initialcontact, when the toe touches the ground, the ground pushes posteriorlyon the foot and the foot pushes anteriorly on the ground. The calf shankwhich has increased forces and momentum is forced into even greaterflexion and downward movement than the initial contact foot flat runner.As a consequence to these forces, the foot's long arch concavity isloaded by expansion and the calf shank is loaded by expansion. Theseexpansion forces are resisted to a greater extent than all the otherpreviously mentioned forces associated with running. As a consequence,the dynamic response capability of the foot is proportional to the forceapplied. The human tibia fibula calf shank response is only associatedwith the energy force potential—it is a straight structure and it cannotstore energy. These expansion forces in the prosthetic foot of theinvention in sprinting are greater in magnitude than all the otherpreviously mentioned forces associated with walking and running. As aconsequence, the dynamic response capability of the foot is proportionalto the applied forces and increased amputee athletic performance, ascompared with human body function, is possible.

The prosthetic foot 53 depicted in FIG. 25 is like that in FIG. 3 exceptfor the adjustable fastening arrangement between the calf shank and thefoot keel and the construction of the upper end of the calf shank forconnection to the lower end of a pylon. In this example embodiment, thefoot keel 54 is adjustably connected to the calf shank 55 by way ofplastic or aluminum coupling element 56. The coupling element isattached to the foot keel and calf shank by respective releasablefasteners 57 and 58 which are spaced from one another in the couplingelement in a direction along the longitudinal direction of the footkeel. The fastener 58 joining the coupling element to the calf shank ismore posterior than the fastener 57 joining the foot keel and thecoupling element. By increasing the active length of the calf shank inthis way, the dynamic response capabilities of the calf shank itself areincreased. Changes in alignment are made in cooperation withlongitudinally extending openings in the calf shank and foot keel as inother example embodiments.

The upper end of the calf shank 55 is formed with an elongated opening59 for receiving a pylon 15. Once received in the opening, the pylon canbe securely clamped to the calf shank by tightening bolts 60 and 61 todraw the free side edges 62 and 63 of the calf shank along the openingtogether. This pylon connection can be readily adjusted by loosening thebolts, telescoping the pylon relative to the calf shank to the desiredposition and reclamping the pylon in the adjusted position by tighteningthe bolts.

The prosthetic foot 70 according to a further embodiment of theinvention is depicted in FIG. 32. The prosthetic foot comprises a footkeel 71, a calf shank 72 and a coupling element 73. The prosthetic foot70 is similar to the prosthetic foot 53 in the embodiment of FIGS.25–27, except that the calf shank 72 in the prosthetic foot 70 is formedwith a downward, convexly curved lower end 74 which extends upwardly,and initially anteriorly on the foot keel 71 into a reversely curvedportion 75 of the calf shank leading to an upstanding upper end 76thereof As shown in more detail in FIGS. 28–31, the calf shank 72 isgenerally parabola shaped at its lower end with the smallest radius ofcurvature thereof located at the lower end.

The reversely curved portion 75 of the calf shank has a posteriorlyfacing surface 77 which is provided with a plurality of longitudinallyextending grooves 78 and fins 79 thereon. The fins and groovesfacilitate resilient compression of the calf shank while resistingexpansion thereof in response to forces on the calf shank during use ofthe prosthetic foot. In the example embodiment, the longitudinallyextending grooves and fins are S-shaped, but could have otherconfigurations, for example the grooves and fins could be linear. As inthe previous embodiments, releasable fasteners 80 and 81 andlongitudinally extending openings 82 and 83 in the calf shank and footkeel permit adjustment of the relationship of the respective, convexlycurved surfaces of the foot keel and calf shank to tune the performanceof the prosthetic foot. These convexly curved surfaces include a dorsalsurface of a midfoot portion of the foot keel and the downward, convexlycurved and anteriorly facing surface of the calf shank as in theprevious embodiment. The relationship of these curves and theperformance of the prosthetic foot have been explained with reference toFIGS. 1 and 2 of the drawings and related discussion above. The calfshank 72 and prosthetic foot 70 lend themselves to the use with acosmetic covering 84 in the shape of a human foot and lower leg as shownin FIG. 32. The cosmetic covering is located over the foot keel and atleast the lower end of the calf shank with the calf shank risingupwardly from the foot keel within the lower leg covering.

This concludes the description of the example embodiments. Although thepresent invention has been described with reference to a number ofillustrative embodiments, it should be understood that numerous othermodifications and embodiments can be devised by those skilled in the artthat will fall within the spirit and scope of the principles of thisinvention. More particularly, reasonable variations and modificationsare possible in the component parts and/or arrangements of the subjectcombination arrangement within the scope of the foregoing disclosure,the drawings, and the appended claims without departing from the spiritof the invention. For example, the several features of the invention inthe various embodiments can be used together or substituted one for theother. The coupling element of the prosthetic foot could also be made ofa resilient material, such as of carbon fiber and a high strengthpolyurethane material, and shaped to impart subtalar joint functionalmotion outcome potential. Further, the components of calf shank,coupling element and foot keel could be integrally formed as a one piece(non-adjustable) prosthetic foot for low cost, or as a two pieceprosthetic foot providing at least some adjustability, according to theinvention. In addition to variations and modifications in the componentparts and/or arrangements, alternative uses will also be apparent tothose skilled in the art.

1. A prosthetic foot comprising: a longitudinally extending foot keel; a calf shank secured to the foot keel at a lower end thereof and extending upwardly from the foot keel; wherein the lower end of the calf shank is downward, convexly curved and extends upwardly, and initially anteriorly therefrom into a reversely curved portion of the calf shank leading to an upstanding upper end thereof; wherein the reversely curved portion of the calf shank has a posteriorally facing surface which is provided with a plurality of S-shaped longitudinally extending grooves and fins formed thereon to facilitate resilient compression thereof in response to forces on the calf shank during use of the prosthetic foot.
 2. The prosthetic foot according to claim 1, wherein the lower end of the calf shank is generally parabola shaped with the smallest radius of curvature thereof located at the lower end.
 3. The prosthetic foot according to claim 1, wherein the calf shank extends upwardly from the foot keel above a hindfoot portion and the posterior part of a midfoot portion of the foot keel.
 4. The prosthetic foot according to claim 1, further comprising a cosmetic covering in the shape of a human foot and lower leg, the cosmetic cover being located over the foot keel and at least the lower end of the calf shank with the calf shank rising upwardly from the foot keel within the lower leg covering.
 5. The prosthetic foot according to claim 1, further comprising an adjustable fastening arrangement securing the calf shank to the foot keel, the fastening arrangement permitting adjustment of the relationship of the foot keel and calf shank to tune the performance of the prosthetic foot.
 6. The prosthetic foot according to claim 5, wherein the adjustable fastening arrangement includes at least one releasable fastener and a longitudinally extending opening in the foot keel through which the fastener extends to permit adjustment of the alignment of the calf shank and foot keel in the longitudinal direction of the foot keel.
 7. The prosthetic foot according to claim 1, wherein the calf shank is secured to the foot keel by way of a coupling element.
 8. The prosthetic foot according to claim 1, wherein the calf shank and foot keel have respective convexly curved surfaces whose radii and relationship affect a dynamic response capability and motion outcome of the prosthetic foot in gait, the respective convexly curved surfaces including a dorsal surface of a midfoot portion of the foot keel and the downward, convexly curved and anteriorly facing surface of the calf shank.
 9. The prosthetic foot according to claim 1, wherein the convexly curved lower end of the calf shank has a radius of curvature which increases as the calf shank extends upwardly from its curved lower end.
 10. A prosthetic foot comprising: a longitudinally extending foot keel having a forefoot portion at one end, a hindfoot Portion at an opposite end and an upwardly arched midfoot portion extending between the forefoot and hindfoot portions; a coupling element connected to the upwardly arched midfoot portion of the foot keel by a first releasable fastener, the coupling element extending posteriorly in the longitudinal direction of the foot keel to where the coupling element is spaced above the hindfoot portion of the foot keel; a resilient, upstanding calf shank having a lower end connected to the foot keel by way of the coupling element to form an ankle joint area of the foot, and an upper end to connect with a supporting structure on an amputee's leg, the lower end of the calf shank being connected to the coupling element by a second releasable fastener spaced posteriorly in the longitudinal direction of the foot keel from the first releasable fastener for increasing the active length and dynamic response capability of the calf shank; wherein the lower end of the calf shank is downward, convexly curved and extends upwardly, and initially anteriorly therefrom into a reversely curved portion of the calf shank leading to the upper end thereof.
 11. The prosthetic foot according to claim 10, further comprising an adjustable fastening arrangement to permit adjustment of the alignment of the calf shank and the foot keel with respect to one another in the longitudinal direction of the foot keel for tuning the performance of the prosthetic foot.
 12. The prosthetic foot according to claim 11, wherein the adjustable fastening arrangement includes a longitudinally extending opening in the foot keel through which the first releasable fastener extends to permit said adjustment of the alignment of the foot keel and calf shank.
 13. The prosthetic foot according to claim 10, wherein the convexly curved lower end of the calf shank has a radius of curvature which increases as the calf shank extends upwardly from its curved lower end.
 14. The prosthetic foot according to claim 10, wherein the lower end of the calf shank is generally parabola shaped with the smallest radius of curvature thereof located at the lower end.
 15. The prosthetic foot according to claim 10, further comprising a cosmetic covering in the shape of a human foot and lower leg, the cosmetic covering being located over the foot keel and at least the lower end of the calf shank with the calf shank rising upwardly from the foot keel within the lower leg covering.
 16. A prosthetic foot comprising: a longitudinally extending foot keel; a coupling element connected to the foot keel; a resilient, upstanding calf shank having a lower end connected to the foot keel by way of the coupling element to form an ankle joint area of the foot, and an upper end to connect with a supporting structure on an amputee's leg; wherein the lower end of the calf shank is downward, convexly curved and extends upwardly, and initially anteriorly therefrom into a reversely curved portion of the calf shank leading to the upper end thereof; wherein the reversely curved portion of the calf shank has a posteriorly facing surface which is provided with a plurality of S-shaped longitudinally extending grooves and fins formed thereon to facilitate resilient compression of the calf shank while resisting expansion thereof in response to forces on the calf shank during use of the prosthetic foot.
 17. A calf shank for a prosthetic foot comprising: an elongated, semi-rigid resilient member having an outward convexly curved portion at one end of said member for attachment to a foot keel to form an ankle area of the prosthetic foot, an opposite end of said member to connect with a supporting structure on an amputee's leg, and wherein said convexly curved portion at said one end of said member extends from the one end and into a reversely curved portion of the calf shank leading to the opposite end; wherein the reversely curved portion of the calf shank has a conversely curved face with a plurality of S-shaped longitudinally extending grooves and fins formed thereon to facilitate resilient compression of the calf shank while resisting expansion thereof in response to forces on the calf shank during use of the calf shank in a prosthetic foot.
 18. The calf shank according to claim 17, further comprising a fastening arrangement including a longitudinally extending opening in said convexly curved one end of said member along which a fastener for connecting said calf shank to a foot keel can be slid.
 19. The calf shank according to claim 17, wherein the convexly curved one end has a generally parabola shape with the smallest radius of the curvature located at the one end.
 20. The calf shank according to claim 17, wherein the convexly curved one end has a radius of curvature which increases as the calf shank extends from the one end. 